tube monoblocks and preamp recommendations

For these speakers, you don't need a 100WPC to effectively drive these.  I would suggest a high quality tube integrated amp like a Manley Stingray or one by Audio Research. 

I was under the impression that the Altec 19's  had about a 100db sensitivity rating which means they could easily be driven to very high levels by a flea watt amp, but that doesn't mean they have to be. I used a 50w class A solid state amp with mine and was quite happy. One problem that such a high sensitivity rating creates is that any noise in your source, pre-amp, or amp will be much more apparent. It would be essential (for me anyway) to insure that the pre-amp was very low noise, something that is difficult to obtain from many tube pre-amp's, and this issue is exacerbated when you are driving an amp with a high sensitivity combined with a pre-amp with a high output. Personally I would be looking for an integrated amp which would (should) solve the interface issues dealing with noise.

If I had my Altec's back (and I'd love to hear them again but I just don't have a room big enuf) I'd probably start out with a Primaluna Dialogue Integrated (One or Two) which has about 36wt in uni-linear and 20 wts in triode (costs about 1500 to 2000 used) for a  more modern tube sound with some residual warmth with the right tubes. These amps are very tunable by simply changing tubes (big and small) using new production tubes. And, best of all, they are sort of idiot proof, both by virtue of their auto bias circuit and their tube protection circuits. IMHO, an ideal starting point (and potentially finishing point) in your quest. 

FWIW, I think Quicksilver has some excellent products. Unfortunately they don't make an integrated unit so you must deal with the matching issues I mentioned above as well as the substantially increased cost.

A rogue audio rp1 and stereo 100 amplifier would be very close to your price point and absolutely sound fantastic with those Altec speakers

With the model 19's , a simple low wattage amp will blow you out of your loft, if that's what you want.
I do like to exercise my Altecs once in a while.

We have a lot of horn customers. At 100db, its nice to have a little power behind the speaker, but in most rooms what that means is likely not going to be more than about 60 watts. For that matter, you'll do fine with only 30- and especially if you are going to use a transformer-coupled tube amp, 30 watts or so is where the best performing tube amps are. More than that in a push-pull design and bandwidth becomes limited.

You could also use an SET, but in many rooms most SETs will not have enough power. With SETs you want to have the speaker efficiency such that the amp does not need to make more than about 20% of its rated power; this is to keep distortion down (SETs typically make about 10% distortion at full power, which can color their presentation, but at much lower powers their distortion becomes hard to detect even with excellent test equipment).

FWIW my speakers at home are 98 db and 16 ohms; I find 80 watts to be an ideal amount of power. 99 44/100% of the time its impossible to clip the amps.

So a lot depends on your room size and how lively it is, as well as how far you will be from the speakers and your own listening habits. If I were you before pulling the trigger on any amplifier I would audition a number of amplifiers using a list of cuts from your music library that show off various aspects of what a stereo should do: soundstage, dynamics, bass impact, detail and so on.